A portable cellular telephone typically includes a housing which contains a speaker, a microphone, a keypad, a display, and an antenna. A printed circuit board containing the electronic circuitry necessary to perform the functions of the cellular telephone is enclosed within the housing. The housing includes a number of openings for keys and buttons that allow ingress of water if used in a rainy environment. If water does penetrate into the interior of the housing, it may cause damage to the electronic circuits contained within the housing.
In certain markets, such as Japan, it is essential for the phone to be able to operate in the rain with no damage. A number of methods have been used in the past to prevent the entry of water into the housing. For example, one solution which has been tried is to design the buttons to seal tightly against the housing. This solution works fairly well when the buttons are in their normal position, however, is still vulnerable to water intrusion when the buttons are pressed. Another solution which has been tried is to design elaborate seals around any openings for buttons or keys. This solution is generally available only when the phone is originally designed for wet weather service. In cases where an existing design is being modified for new markets with stringent water damage requirements, it is not possible to provide complete protection against water damage without extensive (and expensive) redesign of the product.
A third solution which has been tried in the past is to apply conformal coatings to the electronic circuitry within the housing. Such coatings are expensive and can make it difficult to service or repair the electronics.
Accordingly, there is a need for a new type of water protection for electronic devices, such as cellular phones which can be incorporated into existing designs and yet provide some measure of protection against water in wet weather environments.